Question

If (3, 1) is the point of intersection of lines $ax+by=7$ and $bx+ay=5,$ find the value of $a$

• A. 2
• B. 4
• C. 5
• D. 6

Answer 1

The correct option is A 2

(3,1) lies on ax + by = 7
Thus, 3a + b = 7..........eq(i) and
it lies on bx + ay = 5
Thus, 3b + a = 5............eq.(ii)
Multiply (i) by 3 and subtractng both equations
$9a+3b=21$
$a+3b=5$
$-$ $-$ $-$
_______________ ________
8a = 16
a = 2
hence, b = 1
Hence value of a is 2