Question

I am so desperate, please help! i have to factor this equation. 21r^2 - rs - 2s^2
As well as solve this one in any way: x^4-21x^2-100=0
Please! The questions are due in 10-15 minutes!

Answer 1

(3r-s) (7r+2s) for the first one.

(x-5) (x+5) (x^2+4) = 0
x = 5 and x = -5 for the second one.

:)

Answer 2

tlau, how did you get the answer?

Answer 3

Factor by inspection. Valid method.

Answer 4

x^4 -21x^2 -100 =0 note x^2=y
so than y^2 -21y -100=0
y_1,_2=(21+/- sqrt(441+400))/2=(21+/- sqrt(841))/2 =

Answer 5

wouldn't the answer to the second one also be -4 as well?

Answer 6

You can't square root a negative number. Have you done imaginary numbers?

Answer 7

x^2 = -4
No real number x can be squared to get -4. Any number squared positive or negative is positive.

Answer 8

I did 2 years ago. i'm having to relearn everything as I am starting pre-cal, but now I understand. Thank you very much!

Answer 9

No problem. :D