Question

If 7x + 8y=10 and 9x - ky = 20 has a unique solution, then which of the following cannot be the value of k ?
(1) -72/7
(2) 81/7
(3) -67/9
(4) 64/9

Only one option is correct.
Need qualitative answer with good explanation.

Answer 1

hey mate
happy new year ❤️✌️ you
7x+8y=10
7x=10-8y
X=(10-8y)/7. (1)......
9x-ky=20
put value of X in eq
9(10-8y)/7-ky=20
{ 9(10-8y)-7ky }/7 =20
{90-72y-7ky}=140
-72y-7ky =50
-y(72+7k) =50
y(72+7k)= -50 (2)....
y =-50/(72+7k)
put value y in eq.(2)...
so,y=1
put value y in eq.
so,k=-72/7

Answer 2

Heyy mate ❤✌✌❤

Here's your Answer..