Question 190529
Well, you could use the following property: the sum of the three angles of any triangle is 180 degrees.



So let x, y, and z be the three angles of a triangle



According to the given property, this means that {{{x+y+z=180}}}



Since " one angle of a triangle is 90 degrees", this means that we'll let {{{x=90}}}



{{{x+y+z=180}}} Start with the given equation



{{{90+y+z=180}}} Plug in {{{x=90}}}



{{{y+z=180-90}}} Subtract 90 from both sides



{{{y+z=90}}} Combine like terms.



So this shows that the sum of the other two angles is 90 degrees.