$X$-rays are used in:

$\left(\frac{1+i}{1-i}\right)^4+\left(\frac{1-i}{1+i}\right)^4$ is equal to

The combined equation of the bisectors of the angles between the lines joining the origin to the points of intersection of the curve $x^2+y^2+xy+x+3y+1=0$ and the line $x+y+2=0$ is

Zener breakdown takes place if

If $A$ is any set,then:

In any $\triangle ABC$,$a(b \cos C - c \cos B)$ equals