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Given, x2-yx = 7.............. (i) ⇒ xy=x2-7 ⇒ y = x2-7x ⇒y = x- 7x . . . . . . . . . (ii)
Another equation is y2+xy = 30 . . . . . . . . . . (iii)
Adding equation (i) and (iii) we get
x2 - xy = 7 y2 + xy = 30 x2 + y2 = 37. . . . .(iv)
Now, putting the value of y in equation (iv) we get
x2 + x - 7x2 = 37 ⇒ x2 + x2 - 2 × x × 7x + 7x2 = 37 ⇒ 2x2 -14 + 49x2 = 37 ⇒ 2x2 + 49x2 = 51 ⇒ 2x4 + 49x2 = 51 ⇒ 2x4 - 51x2 + 49 = 0 ⇒ 2x4 - 2x2 - 49x2 + 49 = 0 ⇒2x2 x2 - 1 - 49 x2 - 1 = 0 ⇒ x2 - 1 2x2 - 49 = 0 Here, x2 - 1 = 0 ⇒x2 = 1 ⇒x = 1 ∴x =1 And, 2x2 - 49 = 0 ⇒x2 = 492 ∴ x = 492 = 72 Thus we get z = 1, 72 When x = 1, then y = 1 - 71 = 1 - 7 = -6 And when x = 72, then y = 72 - 77 = 72 - 71 × 27 =72 - 2 = 7-222 = 7-22= 52 ∴ x,y = 1, -6 or 72, 52ans.
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