Algebra
- If a2 + b2 = 2 and c2 + d2 = 1, then the value of (ad – bc)2 + (ac + bd)2 is
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(ad – bc)2 + (ac + bd)2
= a2d2 + b2c2 – 2abcd + a2c2 +
b2d2 + 2abcd
= a2d2 + b2c2 + a2c2 +
b2d2
= a2d2 + b2d2 + b2c2 + a2c2
= d2(a2 + b2) + c2(b2 + a2)
= (a2 + b2) (c2 + d2)
= 2 × 1 = 2Correct Option: D
(ad – bc)2 + (ac + bd)2
= a2d2 + b2c2 – 2abcd + a2c2 +
b2d2 + 2abcd
= a2d2 + b2c2 + a2c2 +
b2d2
= a2d2 + b2d2 + b2c2 + a2c2
= d2(a2 + b2) + c2(b2 + a2)
= (a2 + b2) (c2 + d2)
= 2 × 1 = 2
- If x2 = y + z, y2 = z + x, z2 = x + y,
then the value of 1 + 1 + 1 is; x + 1 x + 1 z + 1
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Tricky Approach
x2 = y + z
⇒ x2 + x = x + y + z
⇒ x (x + 1) = x + y + z ....(i)
Similarly,
y (y + 1) = x + y + z .........(ii)
and, z (z + 1) = x + y + z ...(iii)∴ 1 + 1 + 1 x + 1 x + 1 z + 1 = x + y + z x + y + z x + y + z z + y + z ⇒ x + y + z = 1 x + y + z Correct Option: B
Tricky Approach
x2 = y + z
⇒ x2 + x = x + y + z
⇒ x (x + 1) = x + y + z ....(i)
Similarly,
y (y + 1) = x + y + z .........(ii)
and, z (z + 1) = x + y + z ...(iii)∴ 1 + 1 + 1 x + 1 x + 1 z + 1 = x + y + z x + y + z x + y + z z + y + z ⇒ x + y + z = 1 x + y + z
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If p + q = 10 and pq = 5, then the numerical value of p + q will be q p
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p + q = p² + q² p q pq = (p + q) - 2pq pq = 100 - 2 × 5 = 90 = 18 5 5 Correct Option: D
p + q = p² + q² p q pq = (p + q) - 2pq pq = 100 - 2 × 5 = 90 = 18 5 5
- If a1/3 =11, then the value of a2 – 331a is
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a1/3 =11 ⇒ a = 113 = 1331
∴ a2 – 331a = a(a – 331)
= 1331 (1331 – 331)
= 1331 × 1000 = 1331000Correct Option: B
a1/3 =11 ⇒ a = 113 = 1331
∴ a2 – 331a = a(a – 331)
= 1331 (1331 – 331)
= 1331 × 1000 = 1331000
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If 1.5x = 0.04y, then the value of y2 − x2 is y2 + 2xy + x2
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1.5x = 0.04y
⇒ x = 0.04 = 4 = 2 y 1.5 150 75 ⇒ y = 75 x 2 Now, y2 − x2 y2 + 2xy + x2 = (y − x)(y + x) (y + x)2 = y − x y + x = y − 1 x y + 1 x = 75 − 1 2 75 + 1 2 = 73 77 Correct Option: B
1.5x = 0.04y
⇒ x = 0.04 = 4 = 2 y 1.5 150 75 ⇒ y = 75 x 2 Now, y2 − x2 y2 + 2xy + x2 = (y − x)(y + x) (y + x)2 = y − x y + x = y − 1 x y + 1 x = 75 − 1 2 75 + 1 2 = 73 77