# Subs

• Nov 30th 2007, 05:27 PM
Nightfire
Subs
i had a pretest today, and the bonus question involved subs..i dont know how to type them, but its the opposite of powers. the real test will probably have a similar bonus question, and i need to get all the points i can to make up for a test i bombed recently, so can someone please give me a quick lesson on sub qualities?
also, the question was something like this:
solve for b
A=y-(b sub1+ b sub2)
• Nov 30th 2007, 06:43 PM
colby2152
Quote:

Originally Posted by Nightfire
i had a pretest today, and the bonus question involved subs..i dont know how to type them, but its the opposite of powers. the real test will probably have a similar bonus question, and i need to get all the points i can to make up for a test i bombed recently, so can someone please give me a quick lesson on sub qualities?
also, the question was something like this:
solve for b
A=y-(b sub1+ b sub2)

I have never heard of that terminology, but I imagine $\displaystyle b subN = \frac{1}{b^N}$. Therefore, so solve b for your question would go like this...

$\displaystyle A = y - \frac{1}{b} - \frac{1}{b^2}$
$\displaystyle A - y = - \frac{1}{b} - \frac{1}{b^2}$

Multiply both sides by -1...
$\displaystyle y - A = \frac{1}{b} + \frac{1}{b^2}$

Multiply both sides by $\displaystyle b^2$
$\displaystyle b^2(y - A) = b + 1$
$\displaystyle b^2(y - A) - b - 1 = 0$

Use quadratic formula to solve for b
$\displaystyle b=\frac{1 \pm \sqrt{1 - 4(-1)(y - A)}}{2(y - A)}$