Gọi N là Ly ⊥ Mz
LMN + LMz = $180^{o}$ (kề bù)
LMN = $180^{o}$ - LMz
LMN = $180^{o}$ - $112^{o}$
LMN = $68^{o}$
Xét ΔLMN có:
LMN + LNM + MLN = $180^{o}$ (tổng 3 góc trong Δ)
$68^{o}$ + $90^{o}$ + MLN = $180^{o}$
MLN = $180^{o}$ - ($68^{o}$ + $90^{o}$)
MLN = $22^{o}$
Vì x + MLN = $180^{o}$ (kề bù)
⇒ x = $180^{o}$ - MLN
⇒ x = $180^{o}$ - $22^{o}$
Vậy x = $158^{o}$