Cách làm cho bạn:
Ta có:
$\cos A=\frac{b^{2}+c^{2}-a^{2}}{2bc}=\frac{85^{2}+54^{2}-52,1^{2}}{2.85.54}\approx 0,81$
=> $\cos A=\frac{b^{2}+c^{2}-a^{2}}{2bc}=\frac{85^{2}+54^{2}-52,1^{2}}{2.85.54}\approx 0,81$
$\widehat{A}\approx 36^{\circ}$
$\cos B=\frac{a^{2}+c^{2}-b^{2}}{2ac}=\frac{52,1^{2}+54^{2}-85^{2}}{2.52,1.54}\approx -0,28$
=> $\widehat{B}\approx 106^{\circ}28'$
=> $C=\widehat{C}=180^{\circ}-\widehat{A}-\widehat{B}=180^{\circ}-36^{\circ}-106^{\circ}28'=37^{\circ}32'$
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