<span>cos 36 cos 24 - sin 36 sin24=cos(36+24)=cos60=1/2</span>
1) <span>(77838+3702)=81540
2) </span><span>(280*804-224214)=906
3)</span>81540:906=90
4)90*30=2700
5) 2700+80=2780
<span>3(a+2b)-a=3а+6b-a=2a+6b=2(a+3b)=2*1.1=2.2
2.4(3x+5y)-4y=7.2x+12y-4y=7.2x+8y=8(0.9x+y)=8*2=16
8(0.5a+3b)+8a=4a+24b+8a=12a+24b=12(a+2b)=12*2.5=30
3(0.6m+5n)-3n=1.8m+15n-3n=1.8m+12n=6(0.3m+2n)=6*4=24</span>
4 2/5 4 3/4 7 5/7 5 5/8 13 2/5 17 2/3