Step-by-step explanation:
let x be the number
x²+4x=21
x²+4x-21=0
(x-3)(x+7)=0
x=3, x=-7
when x=-7
-7²+4(-7)=21
21=21
when x=3
3²+4(3)=21
both are true so except 3 the answer is also -7
Copyright © 2024 EHUB.TIPS team's - All rights reserved.
Answers & Comments
Step-by-step explanation:
let x be the number
x²+4x=21
x²+4x-21=0
(x-3)(x+7)=0
x=3, x=-7
when x=-7
-7²+4(-7)=21
21=21
when x=3
3²+4(3)=21
21=21
both are true so except 3 the answer is also -7