Solve x2 − 8x − 20 = 0.

x = 4, x = −5
x = −4, x = 5
x = 2, x = −10
x = −2, x = 10

Question

Solve x2 − 8x − 20 = 0.

 x = 4, x = −5
 x = −4, x = 5
 x = 2, x = −10
 x = −2, x = 10

anonymous · Answer

@mathmate  @Teddyiswatshecallsme

welshfella · Answer

you need to find 2 numbers whose product = -20 and whose sum = -8

welshfella · Answer

these will be the values of a and b in the factors of the expression
(x + a)(x + b) = 0
you can then find the zeroes

welshfella · Answer

try factoring -10 and see if you can make -8 from 2 of the factors

welshfella · Answer

sorry  thats -20 not -10

anonymous · Answer

Ok I think I understand what you mean...... ok so -10 * 2 = -20....... and then I have to find a way to make -20 equal -8....?

welshfella · Answer

you are on the right track 
 -10 and 2 is right
because  -10 + 2 = -8

welshfella · Answer

so that the factors are 
(x - 10 )(x + 2)

anonymous · Answer

Oh wow that was suprisingly simple.....

welshfella · Answer

yea
when you expand the factors the -10*x and 2*x make -8x

anonymous · Answer

Ah ok thanks man

welshfella · Answer

yw
now to get the zeros you equate to 0
(x - 10)(x + 2) = 0

means that x-10 = 0  or x + 2 = 0

so the zeros are 10 and -2