Answer:
D
Step-by-step explanation:
Using sine ratio in left right angled triangle to find the altitude a of the large triangle which is common to both right triangles and the exact value
sin60° = [tex]\frac{\sqrt{3} }{2}[/tex] , then
sin60° = [tex]\frac{opposite}{hypotenuse}[/tex] = [tex]\frac{a}{7\sqrt{3} }[/tex] = [tex]\frac{\sqrt{3} }{2}[/tex] ( cross- multiply )
2a = 21 ( divide both sides by 2 )
a = [tex]\frac{21}{2}[/tex]
Using the cosine ratio in the right side triangle and the exact value
cos45° = [tex]\frac{1}{\sqrt{2} }[/tex] , then
cos45° = [tex]\frac{adjacent}{hypotenuse}[/tex] = [tex]\frac{a}{x}[/tex] = [tex]\frac{1}{\sqrt{2} }[/tex] ( cross- multiply )
x = [tex]\sqrt{2}[/tex] a = [tex]\sqrt{2}[/tex] × [tex]\frac{21}{2}[/tex] = [tex]\frac{21\sqrt{2} }{2}[/tex] → D
