4cos2a = 4*(2cos^2 a - 1) = 8cos^2 a - 4
8cos^2 a - 4 = 8*1/16 - 4 = 1/2 - 4 = 0,5 - 4 = -3,5
Ответ: -3,5
Sn=2a1+(n-1)d/2 * n
267=108+5d/2 * 6
267=(108+5d )*3
108+5d=89
5d=-108+89
5d=-19
d=-19/5
a6=a1+5d=54-19=35
-<span>√605</span>
<span><span>√294</span></span>
<span><span>-<span>√845</span></span></span>
<span><span><span>-<span>√72</span></span></span></span>
<span><span><span><span>-<span>√50</span></span></span></span></span>
<span><span><span><span><span><span>√80/7</span></span></span></span></span></span>
<span><span><span><span><span><span><span>√5z^2</span></span></span></span></span></span></span>
<span><span><span><span><span><span><span><span>√11t^2</span></span></span></span></span></span></span></span>