In the triangle ABC, the opposite sides of the three inner angles ABC are ABC, and the angle a is 80 °, a & # 178; = B (B + C), and the degree of angle c is calculated

In the triangle ABC, the opposite sides of the three inner angles ABC are ABC, and the angle a is 80 °, a & # 178; = B (B + C), and the degree of angle c is calculated

a^2=b(b+c),
The result of cosine theorem
a^2=b^2+c^2-2bc*cosA,
c^2=a^2+b^2-2ac*cocC,
The above three formulas give B = C * cosa + A * COSC,
From the sine theorem,
a/sinA=b/sinB=c/sinC,
B / C = SINB / sinc = cosa + Sina * COSC / sinc,
It is concluded that cosa * sinc + Sina * COSC = SINB
cos80°*sinC+sin80°*cosC=sin(100°-C),
After finishing, Tanc = (sin100 ° - sin80 °) / (cos100 ° + cos80 °) is finished, and the score is given

In the triangle ABC, a, B and C are the opposite sides of three internal angles a, B and C respectively, a = 2, C = 45 degrees, cos (B / 2) = (2 √ 5) / 5, and the triangle area is calculated

cosB=2(cosB/2)^2-1=3/5
Because 0 degree

Given that the three internal angles a, B and C of a triangle ABC satisfy the formula of angle B + angle C-3, angle a = 0 ° and angle B = 2 angle c, the shape of the triangle is
If the lengths of four sides of a quadrilateral are 3, 7, X and 2, then the value range of X is

So ∠ a ＝ C, so ∠ B = 2 ∠ a, so ∠ a ＝ C, so ∠ a ＋ B ＋ C = 4 ∠ a = 180 ° so ∠ a ＝ C = 45 ° and ∠ B = 90 °. ABC is isosceles RT △ 12 > x > 2

In △ ABC, SINB = sinacosc, where a, B and C are the three internal angles of △ ABC, and the maximum side length of △ ABC is 12, and the sine of the minimum angle is 1 divided by 3
Judging the shape of △ ABC

From the sine theorem and cosine theorem, B / SINB = A / Sina, COSC = (a ^ 2 + B ^ 2-C ^ 2) / (2Ab) and SINB = sinacosc, then B = a × (a ^ 2 + B ^ 2-C ^ 2) / (2Ab), we can get a ^ 2 = B ^ 2 + C ^ 2, we can know that a is right angle, and a = 12, suppose B is the minimum angle, then SINB = 1 / 3, from the sine theorem, a / Sina = B / SINB, that is 12 / 1 = B /