Although I am a liberal arts student, I can tell you ... because the first question is cosA= 1/2, right ... By using the cosine theorem, we can know that B+C -20=bc, and the average value, B+C is greater than or equal to 2 √ (B x C) is not equal to 2bc, so 2bc- so bc is less than. The area is 1/2 bcsinA. . That's 5√3. . . I am exhausted. . I can type word by word! ! ! ! Generally speaking, the maximum value is composed of the average value.