If x = 1 is a common roots of the equations ax2 + ax + 3 = 0 and x2 + x + b = 0, then ab =

Question:

If $x=1$ is a common roots of the equations $a x^{2}+a x+3=0$ and $x^{2}+x+b=0$, then $a b=$

(a) 3
(b) 3.5
(c) 6
(d) −3

Solution:

$x=1$ is the common roots given quadric equation are $a x^{2}+a x+3=0$, and $x^{2}+x+b=0$

Then find the value of $q$.

Here, $a x^{2}+a x+3=0$........(1)

$x^{2}+x+b=0 \ldots$ (2)

Putting the value of $x=1$ in equation (1) we get

$a \times 1^{2}+a \times 1+3=0$

$a+a+3=0$

$2 a=-3$

$a=-\frac{3}{2}$

Now, putting the value of $x=1$ in equation (2) we get

$1^{2}+1+b=0$

$2+b=0$

$b=-2$

Then,

$=3$

Thus, the correct answer is (a)

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