how would i solve these
2007-04-21 10:59:34 · 6 answers · asked by rashawn c 1 in Science & Mathematics ➔ Mathematics
x^2-10x-11=0
(x - 11)(x + 1) = 0
x = 11 or x = -1.
8x^2+11x-10=0
(8x - 5)(x + 2) = 0
x = 5/8 or x = -2.
x^2-4x-21
(x - 7)(x + 3) = 0
x = 7 or x = -3.
2007-04-21 11:06:29 · answer #1 · answered by Anonymous · 0⤊ 0⤋
The usual way, either guess or use the quadratic formula. The first one is by guess. The hint is that if the coefficient of the square term is one , the two factor constants have a product that absolutely equals the quadradic constant term , and if the coefficient of the 1st power term is negative, that term be formed from the differences of these possible factors.
That's alot of words, but lets practice one. In the first expression, you only have 2 real factors, 11 and 1. Since the last term has a negative sign, they will have opposing signs. Since the coefficient of the x term is -10, you want -11 and +1. So your factors are (x-11)(x+1).
The second one is harder, since you have a coefficent on the first term. By experience, your constants in the factors will be either 1 and 10 or 2 and 5. Since the last term is negative, one of each pair will be negative. The x-squared term coefficient has factors of 1 and 8 or 2 and 4. Now you have to figure which pairs give you a +11 as the x coefficient. You can do that
Finally, the last one should be pretty easy. Following the "rules", the possible factors are 1 and 21 or 3 and 7. One of each will be negative, and the difference between the two needs to equal 4. Well, 3 and 7 look promising, and in fact the factors are (x-7)(x+3).
2007-04-21 11:28:33 · answer #2 · answered by cattbarf 7 · 0⤊ 0⤋
x^2-10x-11=0, x= 11 / 8x^2+11x-10=0, x= -2 / x^2-4x-21=0,x= -3
2007-04-21 11:13:45 · answer #3 · answered by cards733 1 · 0⤊ 0⤋
X^2-10x-11=(x-11)(x+1), x=11 or -1
8X^2+11X-10 doesn't factor easily, so you use the quadratic formula
-b+or- sqrt(b^2-4ac) / 2a
-11+or-(121-4*8*-10) / 2*8
and get x = 5/8 or -2
x^2+4x-21=(x-3)(x+7), x=3 or -7
2007-04-21 11:13:02 · answer #4 · answered by eight_ball8 3 · 0⤊ 0⤋
last 2 first:
8x^2 + 11x - 10 = 0
(8x - 5)(x+2) = 0
x= -2, 5/8
x^2 - 4x - 21 = 0
(x - 3) (x-4) = 0
x = 3, 4
first one - I'm not sure about right now - are you sure you wrote it down correctly?
2007-04-21 11:07:35 · answer #5 · answered by jules0512 2 · 0⤊ 0⤋
How should I know. I hate math!
2007-04-21 11:04:04 · answer #6 · answered by ♥ Amulet 3 · 0⤊ 0⤋