Q21 of 186 Page 3

Find the values of a and b for which the following system of linear equations has infinitely many solutions:

kx + 3y – (k – 3) = 0, 12x + ky – k = 0

Given, pair of equations


kx + 3y – (k – 3) = 0


and 12x + ky – k = 0


On comparing the given equation with standard form i.e. a1 x + b1y + c1 = 0 and a2 x + b2y + c2 = 0, we get


a1 = k, b1 = 3 and c1 = – (k – 3)


and a2 = 12, b2 = k and c2 = – k


For infinitely many solutions,



Here,


…(1)


On taking I and II terms, we get



k2 = 36


k = √36


k = ±6


But k = – 6 not satisfies the last two terms of eqn (1)


On taking II and III terms, we get



3k = k(k – 3)


3k = k2 – 3k


k2 – 3k – 3k = 0


k(k – 6) = 0


k = 0 and 6


Which satisfies the last two terms of eqn (1)


Hence, the required value of k = 0, 6


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