X2-4x-21. factorise​

Answers (1)

By factorisation method or splitting the middle term

-21=-7×3

-7+3=-4 

 {x}^{2}  - 7x + 3x - 21 \\x (x - 7) + 3(x - 7) \\ (x - 7)(x + 3) \\ x  - 7 = 0 \: and \: x + 3 = 0 \\ x = 7 \: and \: x =  - 3

 

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