A triangle has angles of #78°#, #47°#, and #x+65°#. What is the value of #x#?

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Answer 1 · 2016-10-08T22:31:30

#x=-10#

Since the interior angles of all triangles add up to #180^o#, you have to set up an equation that is equal to #180^o#

#78^o + 47^o + (x + 65^o) = 180^o#

Combine like terms

#78^o + 47^o + 65^o = 190^o#

#x + 190^o = 180^o#

Isolate x by subtracting #190^o# on both sides of the equation

#x=-10#

To check the answer, plug -10 back in for x

#78^o + 47^o + (-10 + 65^o) = 180^o#

#125^o + 55^o = 180^o#