Câu d)$cotA+cotB=\frac{cosA}{sinA}+\frac{cosB}{sinB}$$=\frac{sinAcosB+sinBcosA}{sinAsinB}$$=\frac{sin(A+B)}{sinAsinB}$
Câu d)$cotA+cotB=\frac{cosA}{sinA}+\frac{cosB}{sinB}$$=\frac{sinAcosB+sinBcosA}{sinAsinB}$$=\frac{sin(A+B)}{sinAsinB}$
Câu d)$cotA+cotB=\frac{cosA}{sinA}+\frac{cosB}{sinB}$$=\frac{sinAcosB+sinBcosA}{sinAsinB}$$=\frac{sin(A+B)}{sinAsinB}$