An=a1+d(n-1) => a4=a1+3*d; a8=a1+7*d => a1=a4-3*d = 9-3*d; -7=9-3*d+7*d => d=-4; a1=9+12=21; S=(an+a1)/2 * n => S=(-7+21)/2 * 8 = 56
Ответ: 56.
А^2+12а+36-а^2+3а=36+15а
36+15×(-1/15)=36-1=35
Y=√(1-sin²t)/sin t=cos t/sin t=ctg t.
<span> 21 <span>></span> 18,75; 8,006<span><</span> 9,0001; 7,2 <span><</span> 7,2005; 4,009 <span>></span> 3,999.</span>