The solution of an equation R squared = 18.51 squared + r-7.23 squared The answer in our book is about 27.31, but I can't figure out how to work it out Let's talk about the solution of this equation

The solution of an equation R squared = 18.51 squared + r-7.23 squared The answer in our book is about 27.31, but I can't figure out how to work it out Let's talk about the solution of this equation

This is not difficult to understand
r*r=18.51*18.51+r*r-2*r*7.23+7.23*7.23
The square of R is reduced
2 * r * 7.23 move to the left of the equation
394.893 on the right is divided by 2 * 7.23 on the left, and the result is 27.309336, which is about 27.31

The diameter of a circle is 12 decimeters, and the radius is 1 / 4 longer than the original. What is the area of the circle?
Expressed in fractions

（1+1/4）×（1+1/4）=25/16
The area is 25 / 16 of the original

Given: F (n) = sin (n π / 4), find: F (1) + F (2) + +f(100).

F (1) = sin (π / 4) = 1 / radical 2
f(2)=sin(π/2)=1
F (3) = sin (3 π / 4) = 1 / radical 2
f(4)=sin(π)=0
When n is equal to 5, obviously f (n) = - f (n-4)
therefore
`f(1)+f(2)+… +f(100)
=(f(1)+...+f(8))+(f(9)+...+f(16))+...+f(97)+f(98)+f(99)+f(100)
=0+0+0...+f(1)+f(2)+f(3)+f(4)
=1 + radical 2

60 * 15% = (60 + x) * 10%, how to solve this equation
Come on

60*15%=(60+X)*10%
9＝60×10％＋X×10％
9＝6＋0.1X
0.1X＝9－6
0.1X＝3
X＝3÷0.1
X＝30

How much is sin 50 ° and Tan 50 ° respectively

Sine 0.766

The train accelerates on the flat track with an acceleration of 0.98m/s2. A passenger in the carriage reaches out of the window and releases an object from the place 2.5m above the ground. Regardless of the air resistance, the horizontal distance between the object and the passenger is ()
A. 0b. 0.25mc. 0.50md

Let v be the speed of the train when the ball is released. According to h = 12gt2, the time of horizontal throwing motion of the object is t = 2hg = 2 × 2.510 = 22s. The horizontal displacement of the object is X1 = vt. the displacement of the train is x2 = VT + 12at2, then the displacement difference △ x = x2-x1 = 12at2 = 12 × 0.98 × 12S ≈ 0.25m

Aunt Wang raised many chickens and rabbits. It is known that there are 13 more chickens and 16 more feet than rabbits. How many chickens and rabbits are there?

Suppose there are x rabbits, then there are (x + 13) chickens, (x + 13) × 2-4x = 16 & nbsp; & nbsp; & nbsp; & nbsp; 2x + 26-4x = 16 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 2x = 10 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; X = 5, then there are 13 + 5 = 18 chickens and 5 rabbits

The emphasis is on how to transform ∫ X & # 178; · 1 / (x + 1) DX to the next step
The answer is 1 / 2 [(X & # 178; + 1) ln (X & # 178; + 1) - X & # 178;] + C

∫xln(x²+1)dx
=(1/2)∫ln(x²+1)dx²
=(1/2)[x²ln(x²+1)-(x²-ln(x²+1))]+C
=(1/2)(X²+1)ln(x²+1)-(x²/2)+C

How to calculate 3x & # 178; - 32x + 84 = 0 by cross multiplication

Given that the point P (a-1,2a + 4) is symmetric with respect to the origin, the point is in the third quadrant, and the value range of a is obtained

The point P (a-1,2a + 4) is symmetric about the origin, and the point is in the third quadrant
P is in the first quadrant
a-1＞0 a＞1
2a+4＞0 a＞-2
∴a＞1