Explanation:
Given
x² - 9x + 20 = 0
x² - ( 4 + 5) x + 20 = 0
x² - 4x - 5x + 20 = 0
x ( x - 4 ) - 5 (x - 4 ) = 0
(x - 4 ) ( x - 5 ) = 0
Either
x - 4 =0
x = 4
or
x - 5 =0
x = 5
x = 4 and 5
Hope it will help :)
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