<p>Hi!</p>
<p>I've been doing practice tests in the BB and came across 2 math problems I'm not sure of...They are both on page 587, # 19 and 20..
If anyone has their BB with them, please help!
Thank you so much!! >.<</p>
<p>Oh and also another math problem on page 596, #8</p>
<p>If a and b are positive integers and [a^(1/2)b^(1/3)]^6 = 432, what is the value of ab?</p>
<p>A) 6
B) 12
C) 18
D) 24
E) 36</p>
<p>Thanks again!</p>
<p>19, Cross multiply them, only one is different
All of them are af=bc, except a whcih is ac=fb</p>
<p>For 20, I ended up solving all of the algebraic solution of it then substituted one of them variables with a number (a=1) and graphed it on the calculator. A and C had positive x values at zero (or zero) while B was negative. Only other way I could think of is, using logic
I = ab - a
II = ab + b^2 - b
III = ab + ab - a - b</p>
<p>For 8, honestly, I can’t think of any other way to solve this.
I used guess and check basically.
A. Simplified the left side into (a^3)(b^2)=432
B. Since B is squared, I figured something had to be a perfect square, so I began dividing the right side by perfect squares. And the result had to be able to cube rooted (as A is to the 3rd degree)
432/4 = 108 , not a cube root
432/9 = 48, not a cube root
432/16 = 27, cube root of 3
C. So b^2 = 16, a^3=27, therefore b=4, a=3
D. 4 x 3 = 12</p>
<p>^ thank you so much, significa~!</p>
<p>but for III, isn’t it a^2 + ab - a - b?</p>
<p>Yeah, it is, typo, sorry. Anyway I edited the top with what took me forever to get for #8 :o</p>
<p>If a and b are positive integers and [a^(1/2)b^(1/3)]^6 = 432, what is the value of ab?</p>
<p>a^3.b^2 = 432
a^3.b^2 = 2 x 2 x 2 x 2 x 3 x 3 x 3 = 2^4. 3^3 = 4^2.3^3
so a^3.b^2 = 3^3. 4^2
a = 3, b = 4
ab = 12</p>