Answer:
fourth option
Step-by-step explanation:
Since the sides are congruent, then the diagonal divides the square into 2 right isosceles triangles.
Thus the 2 base angles are congruent with measure 45°
Hence y = 45
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Using the cosine ratio in the right triangle and the exact value
cos45° = [tex]\frac{\sqrt{2} }{2}[/tex] , then
cos45° = [tex]\frac{adjacent}{hypotenuse}[/tex] = [tex]\frac{x}{10}[/tex] = [tex]\frac{\sqrt{2} }{2}[/tex] ( cross- multiply )
2x = 10[tex]\sqrt{2}[/tex] ( divide both sides by 2 )
x = 5[tex]\sqrt{2}[/tex]
