If cosx = - 4 / 5 and TaNx > 0, find tanxcos3x / 1-sinx

If cosx = - 4 / 5 and TaNx > 0, find tanxcos3x / 1-sinx

In the first year of senior high school, it seems that this problem is to study the basic relationship of trigonometric functions with the same angle. It should not be cos 3x, but. Cos & # 179; α, which is more appropriate. Of course, 3x can also be used. Here, do it by cos & # 179; α
Cosx = - 4 / 5, and TaNx > 0, so SiNx

Finding the maximum value of function f (x) = (Sina + a) (cosx + a)

☞f(x)=(sinx+a)(cosx+a)
☞f"(x)=cosx(cosx+a)-(sinx+a)sinx=cos2x+a√2*sin(x+π/4)
☞ when x = - π / 4 + 2K π or x = 3 π / 4 + 2K π, K ∈ n +, there is an extreme point
☞ so we get the results at x = - π / 4 + 2K π and x = 3 π / 4 + 2K π, respectively
&#By substituting f (- π / 4) = A & sup2; - 1 / 2 = f (3 π / 4)
☞ this is the minimum value (you can also find a 30 degree substitute for comparison)

What is the minimum period of trigonometric function | Sina | + | cosx |?
|What is the minimum period of SiNx | + | cosx |?
The answer is pi / 2, which is also the result of my drawing, but I can't think of it!

|The period of sina | and | cosx | is pi, and then the period is pi / 2

If LGA and LGB are two real roots of the equation 2x-4x + 1 = 0, then LG (AB)=

If LGA and LGB are two real roots of the equation 2x-4x + 1 = 0, then LG (AB)=
The results of Weida's theorem are as follows
lga+lgb=4/2=2
lga*lgb=1/2
lg(ab)=lga+lgb=2

The image of a certain function passes through the point (- 1,2), and the value of function y decreases with the increase of independent variable x. please write a function relation that meets the above conditions___ ．

∵ y decreases with the increase of X, ∵ K ＜ 0. And ∵ a straight line crosses a point (- 1,2), ∵ the analytic formula is y = - 2x or y = - x + 1, etc. so the answer is: y = - 2x (the answer is not unique)

Six times of a number is 1.8 more than three times of it

A: this number is 0.6

As shown in figure a, the equation of the known ellipse is x ^ 2 / A ^ 2 + y ^ 2 / b ^ 2 = 1 (a > b > 0), and a is the left vertex of the ellipse
If the quadrilateral oabc is a parallelogram and the angle OAB is 45 degrees, then the eccentricity of the ellipse is?

Because oabc is a parallelogram, so ab ∥ OC, then the OC equation is y = x and the elliptic equation is simultaneous. The coordinates of point C are (AB / C, AB / C). Because BC ∥ Ao, the ordinates of B and C are the same, and the abscissa is opposite, that is, B (- AB / C, AB / C). According to ∣ ab ∣ = ∣ OC ∣, from the distance formula between two points, there is the equation √ [(- AB / C + a

The difference of nine tenths minus the number a is equal to the sum of one eighth and two fifths to find the number a (solution of the equation)
Sit down and wait for one minute! Quick bonus points

Let a be X
9/10+x=1/8+2/5
x=-3/8

COS is more or less equal to - √ 3 / 2, expressed in π

cosx=-√3/2
Then x = 2K π ± 5 π / 6

What's the relationship between chord length formula and WIDA theorem? If the known quantity of chord length formula is enough, why should there be this formula? If the direct distance formula is OK, it's better to give me a simple example. When WIDA theorem must be used, can you help me talk about their connection? I just learned to help me talk about it. I'm very grateful

For example, if we know the equation of a circle
Find the equation of the straight line to meet the requirements of the topic
Or the required slope
When I was young
These two formulas are often used
Then you will know
Distance formula between two points
Generally speaking
The calculation is very troublesome