x + 6y = 20 /*(-3)
3x + 3y = 15
- 3x - 18y = - 60
3x + 3y = 15
---------------------------- +
- 15y = - 45
y = 3
x = 20 - 6y = 20 - 6*3 = 20 - 18 = 2
Ответ
(2; 3)
На калькуляторе получилось: 0.99999...
=-243 d^20n^30...........................
2) 2sin60+sin90 = 2*√3/2 + 1 = √3+1.
3)cos П/4- sinП/4 = √2/2 - √2/2 = 0.
4)sin П/2- cos П = 1-(-1) = 2.
5)1+ cos^2a/sin^2a = 1 + ctg²α.
6)1-sin^2a/cos^2a = 1 - tg²α.
7)cos10(градус.)*sin15(градус.) = <span><span><span>
0,984808 *0,258819 =
</span><span>
0,254887.
</span></span></span>8)tg100(градус.)*cos205(градус.) = -ctg 10° * (-cos25°) =
= cos 25° / tg 10° = <span><span><span>
0,906308 / 0,176327 = </span><span>5,139927.
</span></span></span>9)sin 225(градус.) = -sin 45° = -√2/2.
10)cos 4П/3 = cos 240° = -cos 60° = -0,5.