X=-6-8у
5(-6-8у)-2у=12
-----------------
х=-6-8у
-30-40у-2у=12
-----------------
х=-6-8у
-42у=42
----------------
х=-6-8у
у=-1
----------;---
х=-6-8(-1)
у=-1
-------------
х=2
у=-1
37÷160=0.23125
или примерно 0.2
<span>б)sin3b+sin5b
3*b+5*b 3*b - 5b
= 2 * sin------------- * cos --------------- = 2 sin4b*cos(-b)
2 2
140+20 140-20
<span>г)sin140 - sin20 = 2 * </span></span>cos ---------------- * sin ------------- = 2* cos80*sin60
2 2