Between which two numbers, each with three decimal places, does lie?
(a)1.415 and 1.416
(b)1.413 and 1.414
(c)1.414 and 1.415
(d)1.410 and 1.411
Show answer
(c) 1.414 and 1.415
Square the candidates: , which is less than 2, and , which is more than 2. So lies between 1.414 and 1.415. It is not exactly 1.41, so it does not sit between 1.410 and 1.411.
Doubling a square
Question 2
The solid square is the given square. The dashed outer square has double its side, and the tilted square stands on its diagonal. How does the area of the outer square compare with the area of the tilted square?
(a)Four times
(b)Half
(c)Equal
(d)Double
Show answer
(d) Double
The outer square holds all eight congruent triangles and the tilted square holds four of them. So the outer square has double the area of the tilted square.
Doubling a square by rearranging four congruent triangles
Question 3
A square of side 4 units is surrounded by four pieces cut from an identical square along both its diagonals. The area of the new square was worked out as 64 square units by doubling the side to 8 units. What is the correct area of the new square?
(a)between 16 and 32 square units
(b)64 square units
(c)16 square units
(d)32 square units
Show answer
(d) 32 square units
Doubling the side gives a square of 4 times the area, not 2 times. The middle square has area 16 square units, and the four pieces add one more square of 16, so the new square has 32 square units.
Halving the area of a square
Question 4
A square is given. Which drawing inside it gives a square of half the area?
(a)Join the midpoints of the four sides
(b)Draw a square on the diagonal
(c)Draw a square on half of one side
(d)Join the centre to the four corners
Show answer
(a) Join the midpoints of the four sides
The square whose corners are the midpoints of the sides takes half of each quarter of the given square, so it has half the area. A square on half a side has only a quarter of the area, and a square on the diagonal has double.
Finding a missing leg from the hypotenuse
Question 5
A right triangle has a hypotenuse of 17 cm and one shorter side of 8 cm. What is the length of the third side?
(a)15 cm
(b)25 cm
(c)√353 cm
(d)9 cm
Show answer
(a) 15 cm
The hypotenuse is the longest side, so its square is the sum of the other two squares. 17² − 8² = 289 − 64 = 225, and √225 = 15 cm.
Finding the hypotenuse from the two legs
Question 6
The two sides meeting at the right angle are 3 cm and 4 cm. What is the length of the longest side?
(a)12 cm
(b)25 cm
(c)5 cm
(d)7 cm
Show answer
(c) 5 cm
The longest side is opposite the right angle. Its square is 3² + 4² = 9 + 16 = 25, so the side is 5 cm.
Hypotenuse of an isosceles right triangle
Question 7
The two equal sides of an isosceles right triangle are 3 units each. What is the area of the square drawn on its hypotenuse?
(a)9 sq. units
(b)6 sq. units
(c)36 sq. units
(d)18 sq. units
Show answer
(d) 18 sq. units
The square on the hypotenuse has twice the area of the square on an equal side. That square has area 3² = 9, so the answer is twice 9, which is 18 sq. units.
Hypotenuse of the unit isosceles right triangle
Question 8
The two sides meeting at the right angle are both 1 unit. What is the length of the hypotenuse?
(a)1 unit
(b)√2 units
(c)4 units
(d)2 units
Show answer
(b) √2 units
The square drawn on the hypotenuse has twice the area of the unit square, so its area is 2 sq. units. A square of area 2 has side √2, so the hypotenuse is √2 units.
Baudhāyana triples and their scaled versions
Question 9
The Baudhāyana triple (3, 4, 5) is scaled by 10. What is the largest term of the scaled triple?
(a)50
(b)15
(c)no such triple
(d)500
Show answer
(a) 50
Scaling multiplies every term by 10, so (3, 4, 5) becomes (30, 40, 50). It is still a triple: 900 + 1600 = 2500 = 50².
Constructing a square of triple, five-times or difference area
Question 10
A square of side 4 units has a diagonal of units. A right triangle has this side and this diagonal as its two perpendicular sides. What is the side of the square on its hypotenuse?
(a) units
(b)7 units
(c)12 units
(d)48 units
Show answer
(a) units
The square on the hypotenuse has area 16 + 32 = 48 sq units, three times the area 16. Its side is units, which is not a whole number.
Fermat's Last Theorem
Question 11
For exactly one of these equations there are infinitely many solutions in natural numbers . Which equation is it?
(a)
(b)
(c)
(d)
Show answer
(a)
Every Baudhāyana triple, such as (3, 4, 5) and its multiples, solves , so there are infinitely many. For every power above 2, Fermat's Last Theorem says there is none.
Combining two different squares
Question 12
Squares of sides 6 units and 8 units are combined by Baudhāyana's method into one square. What is the side of the new square?
(a)14 units
(b)48 units
(c)10 units
(d)100 units
Show answer
(c) 10 units
The new square's area is 36 + 64 = 100 square units, so its side is √100 = 10 units. The side is the hypotenuse of the right triangle with perpendicular sides 6 and 8.
Squares with corners on a dot grid
Question 13
The dots are 1 unit apart and the grid goes on without end. Which whole numbers can be the area of a square with its corners on the dots?
(a)even numbers only
(b)all whole numbers
(c)square numbers only
(d)sums of two square numbers
Show answer
(d) sums of two square numbers
A side going across and up gives area , and one of , may be 0. So the areas are 1, 2, 4, 5, 8, 9, 10, 13 and so on, and areas such as 3, 6, 7 and 11 never occur.
The Baudhayana-Pythagoras theorem from squares on the sides
Question 14
Squares are drawn on the sides of a right triangle whose shorter sides are 5 and 12. The square on the hypotenuse was given the side 17. What is the correct side of that square?
(a)17
(b)13
(c)169
(d)
Show answer
(b) 13
The side 17 comes from adding 5 and 12. The theorem adds the squares: 25 + 144 = 169, so the square on the hypotenuse has side .
The lotus problem: depth of the lake
Question 15
The tip of a lotus stem is 1 unit above the water. Swayed by a breeze, the tip touches the water 3 units from where it stood. The depth is x, so the whole stem is x + 1. What is the value of ?
(a)3
(b)10
(c)9
(d)1
Show answer
(c) 9
The swayed stem is the hypotenuse, so . Moving across, , which is also .
Common misconception in The Baudhāyana-pythagoras Theorem
For two sides 3 cm and 4 cm, the third side must be 5 cm.
Why it feels right. I recognise the 3–4–5 pattern without looking at the angle.
Right
The square relation holds for the sides of a right triangle.
Worked example
The 3 and 4 sticks can open at different angles. Their far endpoints move apart as the angle opens.
Hinge sticks of lengths 3 and 4.
At 90° their far ends are 5 apart.
Open the angle wider and the gap increases.
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