Let f(x)=5x^2. Find a value A such that the average rate of change of f(x) from 1 to A equals 60.

Question

amistre64 · Answer

the average rate of change is just (f(A) - f(1))/(A-1)

anonymous · Answer

i know!

anonymous · Answer

im getting the wrong answer for some reason though

anonymous · Answer

and im getting frustrated

amistre64 · Answer

$$\frac{5a^2-5.1^2}{a-1}=60$$
$$5a^2-5=60(a-1)$$
$$5a^2-5=60a-60$$
$$5a^2-60a-5+60=0$$
$$5(a^2-120a+11)=0$$

anonymous · Answer

5.1?

amistre64 · Answer

$$a=\frac{1}{2}(12\pm\sqrt{12^2-4(11)})$$

amistre64 · Answer

its easier for me to get to the . then the *

myininaya · Answer

$$\frac{5a^2-5(1)^2}{a-1}=60=> \frac{5(a^2-1)}{a-1}=60$$
$$=>\frac{5(a-1)(a+1)}{a-1}=60 => 5(a+1)=60=> a+1=12$$

amistre64 · Answer

pfft!!  thats cheating, and only gets one of them :)

anonymous · Answer

ITS 11!!!!!!!!!!!!!!! O MY GOD!!!!!!!!!!!!!!!!!!!!!!!!

amistre64 · Answer

144-44 = 100

sqrt100 = 10

12 +- 10
/2      /2

6 +- 5 = 1 and 11?

amistre64 · Answer

cant be 1 so that leaves 11, yeah

myininaya · Answer

a cannot be 1 dear lol

myininaya · Answer

lol

amistre64 · Answer

i was getting to that :)

myininaya · Answer

so my way gets all the possible values of A lol

amistre64 · Answer

not the complex ones :P

myininaya · Answer

shhh lets not go there lol