If the graph of the equations x + y = 0 and 5y + 7x = 24

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If the graph of the equations x + y = 0 and 5y + 7x = 24 intersect at (m, n), then the value of m + n is

On putting y = –x in the equation 5y + 7x = 24,
–5x + 7x = 24
⇒ 2x = 24 ⇒ x = 12 & y = –12
∴ m = x = 12, n = y = –12
⇒ m + n = 12 – 12 = 0