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Find the unknown side in the following triangles

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#### Solution

From ΔXYZ, by Pythagoras theorem,

= YZ^{2} = XY^{2} + XZ^{2}

⇒ XY^{2} = YZ^{2} – XZ^{2}

Z^{2} = 39^{2} – 36^{2}

= 1521 – 1296

= 225 = 15^{2}

z^{2} = 15^{2}

⇒ z = 15

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