Simplification
- If the sum of squares of two real numbers is 41 and their sum is 9, then the sum of cubes of these two numbers is
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Let the two real numbers be x and y.
According to the question,
x2 + y2 = 41
x + y = 9
∴ (x + y)2 = x2 + y2 + 2xy
⇒ 81 = 41 + 2xy
⇒ 2xy = 81 – 41 = 40⇒ xy = 40 = 20 2
∴ x3 + y3 = (x + y)3 – 3xy (x + y)
= (9)3 – 3 × 20 (9)
= 729 – 540 = 189Correct Option: C
Let the two real numbers be x and y.
According to the question,
x2 + y2 = 41
x + y = 9
∴ (x + y)2 = x2 + y2 + 2xy
⇒ 81 = 41 + 2xy
⇒ 2xy = 81 – 41 = 40⇒ xy = 40 = 20 2
∴ x3 + y3 = (x + y)3 – 3xy (x + y)
= (9)3 – 3 × 20 (9)
= 729 – 540 = 189
- Find the least number which must be subtracted from 18265 to make it a perfect square.
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∴ Required answer = 40Correct Option: C
∴ Required answer = 40
- If a perfect square, not divisible by 6, be divided by 6, the remainder will be
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Remainder on dividing 32 = 9 by 6 = 3
Remainder on dividing 42 = 16 by 6 = 4
Remainder on dividing 52 = 25 by 6 = 1Correct Option: C
Remainder on dividing 32 = 9 by 6 = 3
Remainder on dividing 42 = 16 by 6 = 4
Remainder on dividing 52 = 25 by 6 = 1
- The greatest perfect square number of 6 digits is
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Largest 6-digit number = 999999
∴ Required perfect square number = 999999 – 1998 = 998001Correct Option: B
Largest 6-digit number = 999999
∴ Required perfect square number = 999999 – 1998 = 998001
- three numbers are such that their sum is 50, product is 3750 and the sum of their reciprocals is 31/50 .Find the sum of the squares of the three numbers.
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x + y + z = 50 ; xyz = 3750
∴ 1 + 1 + 1 = yz + zx + xy x y z xyz = 31 150 ⇒ xy + yz + zx = 31 xyz 150 = 31 × 3750 = 775 150
∴ (x + y + z )2 = x2 + y2 + z2 + 2(xy + yz + zx)
⇒ (50)2 + x2 + y2 + z2 + 2 × 775
⇒ 2500 = x2 + y2 + z2 + 1550
⇒ x2 + y2 + z2 = 2500 – 1550
= 950Correct Option: C
x + y + z = 50 ; xyz = 3750
∴ 1 + 1 + 1 = yz + zx + xy x y z xyz = 31 150 ⇒ xy + yz + zx = 31 xyz 150 = 31 × 3750 = 775 150
∴ (x + y + z )2 = x2 + y2 + z2 + 2(xy + yz + zx)
⇒ (50)2 + x2 + y2 + z2 + 2 × 775
⇒ 2500 = x2 + y2 + z2 + 1550
⇒ x2 + y2 + z2 = 2500 – 1550
= 950