<span>60²+2*60*2+2²= 3600+240+4=3844</span>
<span /><span><span>79²=</span><span><span>(80-1)²=80²-2*80*1+1²=6400-1600+1=4801</span>
</span></span>
.... ... ... ...
... ... .............
25y^2-20xy+4x^2=(5y-2x)^2
<span> х2+8х+15<0
(x+3)(x+5)<0
=========-5======-3========
++++++++++----------</span>