I have tried answering the following question by squaring everything (I think), but I am not right.

c = $\displaystyle \sqrt{a^2+b^2}$ (Change the subject of

the formula to a)

My try:

$\displaystyle c^2$ = $\displaystyle (a^2)^2+(b^2)^2$

$\displaystyle c^2$ = $\displaystyle a^4+b^4$

$\displaystyle a^4$ = $\displaystyle c^2-b^4$

a = $\displaystyle sqrt[4]{c^2-b^4}$

Can you see my error please?