Question

If 5 is a zero of the quadratic polynomial x2 – kx – 15, then the value of k is : (a) 2 (b) -2 (c) 4 (d) -4​

Answer 1

Answer:

−5 is a root of quadratic equation 2x²+px−15=0

so, 2(−5)²+p(−5)−15=0

=>50−5p−15=0

=>35−5p=0

p=7

now, put p=7 in second quadratic equation,

p(x²+x)+k=0

=>7(x²+x)+k=0

=>7x²+7x+k=0

above equation has equal roots

so,D=b²−4ac=0

=>7²−4×7×k=0

=>7−4k=0

=>k=7/4=1.75

hence, the value of k=1.75

Answer 2

Answer:

k= 2

Step-by-step explanation:

25 - 5k - 15 = 0

5k = 10

k= 2