Question 1136411
{{{ sqrt( x^2 + 21 ) - 2 = x + 1 }}}
{{{ sqrt( x^2 + 21 ) = x + 3 }}}
Square both sides
{{{ x^2 + 21. = x^2 + 6x + 9 }}}
{{{ 21 = 6x + 9 }}}
{{{ 6x = 12 }}}
{{{ x = 2 }}}
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check:
{{{ sqrt( 2^2 + 21 ) - 2 = 2 + 1 }}}
{{{ sqrt( 25 ) - 2 = 3 }}}
{{{ sqrt( 25 ) = 5 }}}
OK