find the value of both missing side ( not just y)
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y = 10(√3)/3
unnamed side = 5(√3)/3
Side ratios in a 30°-60°-90° triangle are 1 : √3 : 2.
Multiplying these by 5/√3 gives ...
... unnamed side : 5 : y = 5/√3 : 5 : 10/√3
Then ...
... unnamed side = 5/√3 = 5(√3)/3
... y = 10/√3 = 10(√3)/3