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In a quadrilateral ABCD shown below it is known that BC is perpendicular to CD, angle A=3x+7, and angle C is 5x-15. given this information, which of the following a degree measure of angle A?(1) 40°(2) 55°(3) 70°(4) 82°

In A Quadrilateral ABCD Shown Below It Is Known That BC Is Perpendicular To CD Angle A3x7 And Angle C Is 5x15 Given This Information Which Of The Following A De class=

Sagot :

We know that

[tex]BC\perp CD[/tex]

Wich means that

[tex]\angle C=90[/tex]

We have an expression, in terms of x, for the values of angles A and C. Knowing the value of C, we just have to clear x from C's expression and replace it in A's:

[tex]\begin{gathered} \angle C=5x-15\rightarrow90=5x-15\rightarrow105=5x\rightarrow x=\frac{105}{5}\rightarrow x=21 \\ \text{Thus, } \\ \angle A=3x+7\rightarrow\angle A=3(21)+7\rightarrow\angle A=63+7\rightarrow\angle A=70 \end{gathered}[/tex]

Hence, Angle A is worth 70°