horizontal parts that cancel because of this mass.

水平方向的力因为这个物体而抵消了
This backpack is not going anywhere horizontally;

重物在水平方向上没有运动
the vertical parts of these two,

这两个力在竖直方向的分力
which will be in fact additive,

应该相加
should cancel the weight of the object.

才能抵消物体的重力
That gives you two simultaneous equations for T1 and T2,

由此可以列出关于 T1 和 T2 的联立方程
and you can fiddle with them,

你可以对它们进行变换
and solve them.

把方程解出来
Well, by the way I should tell you,

我顺便要告诉你们
if you got some equation like

如果得到某个方程类似于
or that - T2 · sin(θ2) is 0,

或者是这一项减去 T2·sin(θ2) 等于 0
and another equation

另一个方程