Question

7 and 3 are the roots of a quadratic equation x^2+kx-21=0.find the value of k

Answer 1

Given :-

When roots are given that means the value of x is given by which if we put we get zero as resultant.

So, x = 7 and x = 3

Putting the value of x = 7

we get,

x² + kx - 21 = 0

( 7 )² + k × 7 - 21 = 0

49 + 7k - 21 = 0

28 + 7k = 0

7k = -28

k = -4

now,

putting x = 3

x² + kx - 21 = 0

( 3 ) ² + k × 3 - 21 = 0

9 + 3k - 21 = 0

- 12 + 3k = 0

3k = 12

k = 4

Now, let's verify

by putting x = 7 and y = -4


x² + kx - 21 = 0

49 - 28 - 21 = 0

49 - 49 = 0

0 = 0

so, k = -4 is correct!!!
when x = 7


now,

putting x = 3 and k = 4

x² + kx - 21 = 0

9 + 12 - 21 = 0

21 - 21 = 0

0 = 0

so, k = 4 is correct !!!
when x = 3

@Altaf

Answer 2

Answer:

This is the solution.

Hope it will help you!!