Question 914179


vertical angles are equal: 

< (1) = < (2) (in fact they are congruent angles)

so, if  measure of < {{{1}}} is {{{63}}}° and measure of < {{{2}}} is {{{4x-9}}}°, than

{{{4x-9=63}}}°  ...solve for {{{x}}}

{{{4x=63+9}}}°

{{{4x=72}}}°

{{{x=72/4}}}°

{{{x=18}}}°

if {{{x=18}}}°, than < {{{2}}} is {{{4x-9=4*18-9=72-9=63}}}°...it proves that < (1) = < (2)  are congruent angles