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Consider the pair of equations: x2−xy−x=22x^{2}-x y-x=22 and y2−xy+y=34y^{2}-x y+y=34. If x>yx>y, then x−yx-y equals

Solution

✅ Correct Option: 1

We have two equations:

x2−xy−x=22x^2 - xy - x = 22 ... (1)

y2−xy+y=34y^2 - xy + y = 34 ... (2)

We need to find x−yx - y when x>yx > y.


We add equation (1) and equation (2):

(x2−xy−x)+(y2−xy+y)=22+34(x^2 - xy - x) + (y^2 - xy + y) = 22 + 34

x2−xy−x+y2−xy+y=56x^2 - xy - x + y^2 - xy + y = 56

Combining like terms:

x2+y2−2xy−x+y=56x^2 + y^2 - 2xy - x + y = 56

Key insight: Notice that we can rearrange this as:

x2+y2−2xy−(x−y)=56x^2 + y^2 - 2xy - (x - y) = 56


The first three terms x2+y2−2xyx^2 + y^2 - 2xy form a perfect square pattern.

Since (x−y)2=x2−2xy+y2(x - y)^2 = x^2 - 2xy + y^2, our equation becomes:

(x−y)2−(x−y)=56(x - y)^2 - (x - y) = 56


Let u=x−yu = x - y. Then our equation becomes:

u2−u=56u^2 - u = 56

u2−u−56=0u^2 - u - 56 = 0


We need to factor u2−u−56=0u^2 - u - 56 = 0.

This can be written as: u(u−1)=56u(u - 1) = 56

We need two consecutive integers whose product is 56.

Let's find factors of 56:

56=1×5656 = 1 \times 56 (difference = 55, not consecutive)

56=2×2856 = 2 \times 28 (difference = 26, not consecutive)

56=4×1456 = 4 \times 14 (difference = 10, not consecutive)

56=7×856 = 7 \times 8 (difference = 1, these are consecutive!)

Since uu and (u−1)(u-1) are consecutive integers with product 56, we have:

u=8u = 8 and u−1=7u - 1 = 7


Since u=x−y=8u = x - y = 8, we have our answer.

We can check that 8×7=568 \times 7 = 56

Also, since x>yx > y, we have x−y>0x - y > 0, so x−y=8x - y = 8 (positive) is correct.

x−y=8x - y = 8

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