## College Algebra 7th Edition

$(r-3s)^2$
RECALL: A perfect square trinomial can be factored using either of the following formulas: (i) $A^2-2AB+B^2=(A-B)^2$ (ii) $A^2+2AB+B^2=(A+B)^2$ The given trinomial can be written as: $=r^2-2(r)(3s)+(3s)^2$ The trinomial is a perfect square. Factor using formula (i) above with $A=r$ and $B=3s$ to obtain: $=(r-3s)^2$