Question : If x + y = 36, then find (x – 27)3 + (y – 9)3.
Option 1: 1
Option 2: 81
Option 3: 2y
Option 4: 0
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Correct Answer: 0
Solution : $x + y = 36$ Formula used: $a^3 + b^3 = (a + b)(a^2 - ab + b^2)$ $⇒ x + y = 36$ $⇒ x + y - 36 = 0$--------(1) $⇒ (x - 27) + (y - 9) = 0$ Let's consider $(x - 27) = a$ and $(y - 9) = b$ $a^3 + b^3 = (a + b)(a^2 + b^2 - ab)$ using the formula, substitute the value of a and b into the equation. $(x - 27)^3 + (y - 9)^3= ( x - 27 + y - 9)((x - 27)^2 - (x - 27)(y - 9) + (y - 9)^2)$ $= (x - 27)^3 + (y - 9)^3 = ( x + y - 36)((x - 27)^2 - (x - 27)(y - 9) + (y - 9)^2)$ Substituting the value of $x + y - 36 = 0$ from equation (1). $⇒ (x - 27)^3+ (y - 9)^3 = (0)((x - 27)^2 - (x - 27)(y - 9) + (y - 9)^2)$ $⇒ (x - 27)^3 + (y - 9)^3 = 0$ $\therefore$ The required value is 0. Hence, the correct answer is 0.
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Question : If $x^{2}+y^{2}+6x+5=4(x-y)$, then $(x-y)$ is:
Option 1: $1$
Option 2: $0$
Option 3: $–1$
Option 4: $4$
Question : If $(x-5)^2+(y-2)^2+(z-9)^2=0$, then value of $(x+y-z)$ is:
Option 1: 16
Option 2: –1
Option 3: –2
Option 4: 12
Question : For what value of k will the expression x6 – 18x3 + k be a perfect square?
Option 1: –9
Option 2: –81
Option 3: 9
Option 4: 81
Question : What is the value of (3x3 + 5x2y + 12xy2 + 7y3), when x = – 4 and y = – 1?
Option 1: – 329
Option 2: – 359
Option 3: – 361
Option 4: – 327
Question : If $x^{3}-y^{3}=81$ and $x-y=3$, what is the value of $x^{2}+y^{2}$?
Option 1: 18
Option 2: 21
Option 3: 27
Option 4: 36
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