Hey!
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Given-: ∆RST≅∆YZX
∠RTS= ∠ZXY
∠RST= ∠XZY
RS=SY
By AAS , they are congruent.
And by C.P.C.T, we are left we just two sides, which ought to be equal. And it is,
TS= XZ
Thus, Option (B) is correct.
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Hope it helps...!!!