[tex]Is\ a\ triangle\ is\ an isosceles\ triangle,\ then:\\\\x+1=-x+7\ \ \ \ |subtract\ 1\ from\ both\ sides\\\\x=-x+6\ \ \ \ \ |add\ x\ to\ both\ sides\\\\2x=6\ \ \ \ \ |divide\ both\ sides\ by\ 2\\\\x=3\\--------------\\The\ base:\\3x-3=3\cdot3-3=9-3=\fbox6\leftarrow answer[/tex]
