# Changing the subject of formua with squares and roots

• Sep 27th 2009, 07:10 AM
Meggomumsie
Changing the subject of formua with squares and roots
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?
• Sep 27th 2009, 07:17 AM
Quote:

Originally Posted by Meggomumsie
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?

HI

you are correct by squarring both sides to get rid of the square root but you worked it out wrongly .

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

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

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

$\displaystyle a=\sqrt{c^2-b^2}$
• Sep 27th 2009, 07:34 AM
Meggomumsie
Dohh!!! (Worried) Yes, I see that now!!! Thanks.