Question 553738
Both sides are perfect squares
{{{ y^2 - 10y + 25 = 49 }}}
{{{ ( y - 5 )^2 = 7^2 }}}
Take square root of both sides
{{{ y - 5 = 7 }}}
{{{ y = 12 }}}
and also
{{{ y - 5 = -7 }}}
{{{ y = -2 }}}
check answers:
{{{ 12^2 - 10*12 + 25 = 49 }}}
{{{ 144 - 120 + 25 = 49 }}}
{{{ 24 + 25 = 49 }}}
{{{ 49 = 49 }}}
OK
{{{ (-2)^2 - 10*(-2) + 25 = 49 }}}
{{{ 4 + 20 + 25 = 49 }}}
{{{ 49 = 49 }}}
OK