Question

20 POINTS! The answer is x=4 and x= -5, how should I word it, saying how he is wrong?

Answer 1

The student took the numbers for the factors 5, -4 for the zeros instead of solving the equation

The zeros are -5, 4

Explanation:

x^2 +x - 20=0

What 2 number multiply to -20 and add to 1

5*-4 = -20

5+-4 = 1

(x+5)(x-4) =0

Using the zero product property

x+5 = 0 x-4 =0

x=-5 x=4

Answer 2

Solution given:

equation is:

x²+x-20=0

doing middle term factorisation

note:we need to get 1 while subtracting factor of the product of constant and coefficient of x².

20*1=20=2*5*2*1

we get 1 while subtracting 5-2*2=5-4

now substitute value 5-4 at coefficient of x

we get

x²+(5-4)x-20=0

now

distribute

x²+5x-4x-20=0

taking common from each two term

x(x+5)-4(x+5)=0

again taking common (x+5) and keeping remaining at another bracket

(x+5)(x-4)=0

either

x+5=0

x=-5

or

x-4=0

x=4

Error is:

x= 4 not -4

x=-5 not 5.