Wu gives the optimal solution of the triangle ABC in the plane region, where a (5,2) B (1,1) C (1,22 / 5) has the maximum objective function z = ax + y (a > 0) Infinitely many, then the value of a is () a, - 5 / 3; B, 3 / 5; C, 4; D, 1 / 4; how is it calculated

Wu gives the optimal solution of the triangle ABC in the plane region, where a (5,2) B (1,1) C (1,22 / 5) has the maximum objective function z = ax + y (a > 0) Infinitely many, then the value of a is () a, - 5 / 3; B, 3 / 5; C, 4; D, 1 / 4; how is it calculated

Z = ax + y is transformed into y = - ax + Z. because a > 0, - A

Let a be the smallest angle in △ ABC and cosa = a − 1A + 1, then the value range of real number a is ()
A. a≥3B. a＞-1C. -1＜a≤3D. a＞0

∵ A is the minimum angle in △ ABC, ∵ obtained from the theorem of sum of internal angles of triangles; The inequality can be reduced to a − 1A + 1 ≥ 12, ① a − 1A + 1 < 1, ②, a − 1A + 1-12 ≥ 0, i.e. a − 32 (a + 1) ≥ 0; a ＜ - 1, or a ≥ 3; ②, a − 1A + 1-1 < 0, i.e. − 2A + 1 < 0, i.e. a ≠ - 1; the solution set of the inequality system is {a | a ≥ 3}

Let a be the minimum angle of △ ABC and cosa = m − 1m + 1, then the value range of real number m is ()
A. m≥3B. m＞-1C. -1＜m≤3D. m＞0

Let a be the minimum angle of △ ABC. According to the inner angle sum formula of triangle, we can get & nbsp; 0 °＜ a ≤ 60 °, 12 ≤ cosa < 1, 12 ≤ m − 1m + 1 < 1, that is, m − 1m + 1 − 12 ≥ 0m − 1m + 1 − 1 < 0, m ＜− 1 & nbsp;, or & nbsp; m ≥ 3M ＞− 1, m ≥ 3