The length of diagonal lines AC and BD of quadrilateral ABCD are m and N respectively. It can be proved that when AC ⊥ BD (as shown in Figure 1), the area of quadrilateral ABCD is s = 12mn. Then when the acute angle between AC and BD is θ (as shown in Figure 2), the area of quadrilateral ABCD is s = () A. 12mnB. 12mnsinθC. 12mncosθD. 12mntanθ

The length of diagonal lines AC and BD of quadrilateral ABCD are m and N respectively. It can be proved that when AC ⊥ BD (as shown in Figure 1), the area of quadrilateral ABCD is s = 12mn. Then when the acute angle between AC and BD is θ (as shown in Figure 2), the area of quadrilateral ABCD is s = () A. 12mnB. 12mnsinθC. 12mncosθD. 12mntanθ

As shown in the figure, let AC and BD intersect at point O. in Figure 1, let BD = m, OA + OC = n, so s quadrilateral ABCD = s △ abd + s △ CBD = 12m · OC + 12m · OA = 12mn; in Figure 2, make AE ⊥ BD at e, CF ⊥ BD at F, because the angle between AC and BD is θ, so AE = OA · sin θ, CF = OC · sin θ, ⊥ s four sides