Question

Which of the following quadratic equations has roots 3, 5 ?
(A) x²-15x+8=0
(B) x²-8x+15=0
(C) x²+3x+5=0
(D) x²+8x-15=0

Answer 1

Hi ,

Substitute 3 , 5 in each quadratic equation,

if it is true then 3 ,5 are roots of that equation.

i ) x² - 15x + 8 = 0

put x = 3 ,

3² - 15 × 3 + 8 = 0

9 - 45 + 8 = 0 ( false )

ii ) x² - 8x + 15 = 0

put x = 3

3² - 8 × 3 + 15 = 0

9 - 24 + 15 = 0

24 - 24 = 0 ( True )

put x = 5 , we get

5² - 8 × 5 + 15 = 0

25 - 40 + 15 = 0

40 - 40 = 0 ( true )

Therefore 3 , 5 are roots of x² - 8x + 15 = 0

Option ( B ) is correct.

I hope this helps you.

: )

Answer 2

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