Two events $A$ and $B$ are independent and equally likely. If $P(A\cup B)=3/4$, then $P(A)=$ ?

Let $P(A)=P(B)=x$.Since $A$ and $B$ are independent, $P(A\cap B)=P(A)\cdot P(B)=x^2$.Using the addition theorem:
$$P(A\cup B)=P(A)+P(B)-P(A\cap B)$$
$$\frac{3}{4}=x+x-x^2$$
$$x^2-2x+0.75=0$$
Using the quadratic formula $x=\frac{-b\pm \sqrt{b^2-4ac}}{2a}$:
$$x=\frac{2\pm \sqrt{4-3}}{2}=\frac{2\pm 1}{2}$$
$x=3/2$ or $x=1/2$.Since probability cannot exceed 1, $x=0.5$.