Algebra
Calculus
Trigonometry
Matrix
Question
Factor the expression
(r−4)(r+5)
Evaluate
r2+r−20
Rewrite the expression
r2+(5−4)r−20
Calculate
r2+5r−4r−20
Rewrite the expression
r×r+r×5−4r−4×5
Factor out r from the expression
r(r+5)−4r−4×5
Factor out −4 from the expression
r(r+5)−4(r+5)
Solution
(r−4)(r+5)
Show Solution
Find the roots
r1=−5,r2=4
Evaluate
r2+r−20
To find the roots of the expression,set the expression equal to 0
r2+r−20=0
Factor the expression
More Steps
Evaluate
r2+r−20
Rewrite the expression
r2+(5−4)r−20
Calculate
r2+5r−4r−20
Rewrite the expression
r×r+r×5−4r−4×5
Factor out r from the expression
r(r+5)−4r−4×5
Factor out −4 from the expression
r(r+5)−4(r+5)
Factor out r+5 from the expression
(r−4)(r+5)
(r−4)(r+5)=0
When the product of factors equals 0,at least one factor is 0
r−4=0r+5=0
Solve the equation for r
More Steps
Evaluate
r−4=0
Move the constant to the right-hand side and change its sign
r=0+4
Removing 0 doesn't change the value,so remove it from the expression
r=4
r=4r+5=0
Solve the equation for r
More Steps
Evaluate
r+5=0
Move the constant to the right-hand side and change its sign
r=0−5
Removing 0 doesn't change the value,so remove it from the expression
r=−5
r=4r=−5
Solution
r1=−5,r2=4
Show Solution