计算。 - = + = - = + =&nbs

1. 计算。
$\text{[math]}$ - $\text{[math]}$ =        $\text{[math]}$ + $\text{[math]}$ =         $\text{[math]}$ - $\text{[math]}$ =
$\text{[math]}$ + $\text{[math]}$ =       $\text{[math]}$ + $\text{[math]}$ =         $\text{[math]}$ - $\text{[math]}$ =
$\text{[math]}$ - $\text{[math]}$ =        $\text{[math]}$ + $\text{[math]}$ =        $\text{[math]}$ - $\text{[math]}$ =