How to draw frequency spectrum with MATLAB I don't know how to generate spectrum. Spectrum is not easy to use in MATLAB. I use 08 version of MATLAB

>> t=-10:0.001:10;
>> x=10*cos(800*pi*t+pi/4)+7*cos(1200*pi*t-pi/3)-3*cos(1600*pi*t);
>> X=fftshift(fft(x));
≫ & gt; & nbsp; FS = linspace (- 1000 / 21000 / 2, length (T));%% 1000 is from 0.001, sampling interval
>> plot(fs,abs(X));
grid on

If 2 / 5 of a is equal to 3 / 7 of B, then a: B = what

2 / 5A = 3 / 7b drop 2 / 5
We get a: B = 15 / 14

The area of a parallelogram made of two identical trapezoids is 400 square centimeters, and the area of one trapezoid is ()
The area of a parallelogram made of two identical trapezoids is 400 square centimeters. The area of one trapezoid is () square centimeters. If the height of the parallelogram is 16 centimeters, then the sum of the top and bottom of the trapezoid and the bottom of the individual is () centimeters

The area of a parallelogram made of two identical trapezoids is 400 square centimeters, and the area of one trapezoid is (200) square centimeters
If the height of the parallelogram is 16 cm, then the sum of the top and bottom of the trapezoid is (25) cm

As shown in the figure, points a (m, M + 1) and B (M + 3, m-1) are the second question on the image with inverse scale function y = K / X
Please don't copy that. I don't understand it,

After calculating the value of M, a (3,4), B (6,2) are known
The slope of AB is K1 = - 2 / 3
A quadrilateral with vertices a, B, m and N is a parallelogram, so the slopes of the two are the same, i.e
The slope of nm is K2 = K1 = - 2 / 3
Let m (m, 0), n (0, n)
K2=-n/m=-2/3
|AB|=13^(1/2)=|MN|=(m^2+n^2)^(1/2)
The upper two types stand together:
m=3 or -3
n=2 or - 2
M(-3,0),N(0,-2)or M(3,0),N(0,2)
Function expression of line Mn
:
y=-2(x-3)/3
or y=-2(x+3)/3

It is known that the quadratic function f (x) = AX2 + BX (a is not equal to 0) satisfies the condition; f (2) = 0 and the equation f (x) = x has equal roots,
If x2-3x-4

∵f(2)=0
∴4a+2b=0 ①
And the equation f (x) = x has equal roots
That is, the discriminant of ax ^ 2 + bx-x = 0 is zero
∴（b-1)^2=0
∴b=1
Substituting ① a = - 1 / 2
∴f(x)=-1/2x^2+x
And because of x2-3x-4

As shown in the right figure, it is known that the area of the isosceles right triangle ABC is 12 square centimeters, and the area of the color part of the figure is calculated
We need formula, not letter formula

The intersection point of the vertical line through D for BC is e, de = 1 / 2Ab = R, 2R * 2R / 2 = 12, R * r = 6
The shadow area on the right is 1 / 4 * π * r * R-1 / 2 * r * r = 3 / 2 π - 3
So the total shadow is three times the shadow on the right
s=3*（3/2π-3）=3*（4.71-3）=5.13

As shown in Figure 1, it is known that hyperbola y = KX (k > 0) and straight line y = k ′ x intersect at two points a and B, and point a is in the first quadrant
(1) If the coordinates of point a are (4,2), then the coordinates of point B are (4,2)_ If the abscissa of point a is m, the coordinate of point B can be expressed as_ (2) as shown in Figure 2, make another straight line L through the origin o, intersect the hyperbola y = KX (k > 0) at two points P and Q, and point P is in the first quadrant. ① it indicates that the quadrilateral apbq must be a parallelogram; ② suppose the abscissa of points a and P are m and N respectively, can the quadrilateral apbq be a rectangle? Could it be a square? If possible, write directly the conditions m, n should meet; if not, explain the reason

(1) ∵ hyperbola and straight line y = k'x are centrosymmetric figures about the origin. They intersect at two points a and B, and the coordinates of B are (- 4, - 2), (- m, - k'm) or (- m, - km); (2) by Pythagorean theorem, OA = M2 + (k'm) 2, OB = (- M) 2 + (- k'm) 2 = M2 + (k'm) 2, ‖ OA = ob

How to find the partial derivative of Z = ln TaNx / y? How is it different from the answer

Fill in the words as they are
Example: three "mouths" constitute (quality) (conduct) (morality)
Three pieces of wood
It is composed of three days
It is composed of three "()"
It is composed of three "()"

Three "Woods" (forest) (gloomy)
Three "days" make up (crystal) (crystal) (crystal)
Three "(gold)" constitute (Xin) (Jinxin) (Xinuo)
Three "(people)" constitute (public) (public) (public)

In the given rectangular coordinate system, draw the image of a linear function y = 1-2x, (1) translate the straight line y = 1-2x upward by 2 units, and find the analytic solution of the parallel straight line

Let y '= y + 2, X' = X
y=y’-2 x=x‘ （1）
x. Y satisfies y = 1-2x (2)
Substituting (1) into (2) yields y '- 2 = 1-2x‘
The result is y '= 3-2x

How to draw frequency spectrum with MATLAB I don't know how to generate spectrum. Spectrum is not easy to use in MATLAB. I use 08 version of MATLAB