Solve each of the following systems of equations by using the method of cross multiplication:
We have,
…(i)
…(ii)
Let 1/(x + y) = p and 1/(x - y) = q. Now,
From equation (i), 5p – 2q + 1 = 0 …(iii)
From equation (ii), 15p + 7q – 10 = 0 …(iv)
From equation (iii), we get a1 = 5, b1 = - 2 and c1 = 1
And from equation (iv), we get a2 = 15, b2 = 7 and c2 = - 10
Using cross multiplication,
⇒
⇒
⇒
⇒ and
⇒ and
⇒ p = 1/5 and q = 1
⇒ and
[∵ p = 1/(x + y) and q = 1/(x - y)]
To solve these, we need to take reciprocal of these equations. By taking reciprocal, we get
x + y = 5 and x – y = 1
Rearranging them again,
x + y – 5 = 0 …(v)
x – y – 1 = 0 …(vi)
From equation (v), we get a1 = 1, b1 = 1 and c1 = - 5
And from equation (vi), we get a2 = 1, b2 = - 1 and c2 = - 1
Using cross multiplication,
⇒
⇒
⇒
⇒ and
⇒ and
⇒ x = 3 and y = 2
Thus, x = 3, y = 2