Question : If $a + 5b = 13$ and $ab = 9$, then find the value of $a^2 + 25b^2$.
Option 1: 69
Option 2: 79
Option 3: 49
Option 4: 59
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Correct Answer: 79
Solution : Given: $ab = 9$ $a + 5b = 13$ $⇒(a + 5b)^2 = 13^2$ $⇒a^2 + 25b^2 + 10ab = 169$ $⇒a^2 + 25b^2 +10×9 = 169$ $⇒a^2 + 25b^2 = 169-90=79$ Hence, the correct answer is 79.
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Question : If $3x-2y=3$ and $xy=9$, then find the value of $3x+2y$.
Option 1: 16
Option 2: 13
Option 3: 14
Option 4: 15
Question : If $a =\cot A+\cos A$ and $b =\cot A-\cos A$, then find the value of $a^2-b^2-4 \sqrt{ab}$.
Option 1: 0
Option 2: –1
Option 3: 1
Option 4: –4
Question : If $(a-b)=9$, and $(a^3-b^3)$ = 4401, find the value of $ab$.
Option 1: 190
Option 2: 112
Option 3: 162
Option 4: 136
Question : If a : b : c = 2 : 3 : 5 and 5b – a + 2c = 115, then what is the value of b?
Option 1: 15
Option 2: 12
Option 3: 6
Option 4: 24
Question : If $a^3+b^3=9$ and $a+b=3$, then the value of $\frac{1}a+\frac{1}b$ is:
Option 1: $\frac{1}2$
Option 2: $\frac{3}2$
Option 3: $\frac{5}2$
Option 4: $–1$
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