Easy math problems! 20 points, good plus!

Solution: 1) cosa = 1-2 sin (squared) (a 2), so sin (squared) (a 2) = 1 5;

cos(b+c)=cos(π-a)=-cosa=-3/5;

So, sin(squared)(a2)-cos(b+c)=1 5+3 5=4 5

In the triangle ABC, a, b, and c are not more than 180 degrees, and because cosa=3 5, sina = 4 5

Because s(triangle abc) = 1 2(ab*ac*sina), ac=5

According to the cosine theorem, BC (squared) = AC (squared) + AB (squared) - 2AC*ab*cosa

So, bc = (root number) 17

Solution:1From cosa = 2 cos 2 (a 2) -1 and cosa = 3 5 gets: cos 2 (a 2) = 4 5, so sin 2 (a 2) = 1-4 5 = 1 5

cos(b+c)=cos(π-a)=-cosa=-3/5

So: sin 2(a 2)-cos(b+c)=1 5+3 5=4 5

2.First of all, it is obtained from cosa=3 5: sina = 4 5

From the formula s=1 2*b*c*sina, we can see that b>0, c>0, s>0, so sina >0

So: sina = 4 5

From the meaning of the title: s=4, ab=c=2, substitute s=1 2*b*c*sina to obtain:

4=1 2*b*2*4 5, so b=5, which is ac=5

Then we can find a from the cosine theorem formula, which is BC

From a2=b2+c2-2bc*cosa:

a^2=5^2+2^2-2*5*2*(3/5)

a^2=25+4-12=17

So a = 17 (17 means root number 17).

i.e. bc = 17

UNFORTUNATELY ... I forgot how to do it ...

After X hours, A and B are kilometers apart.

There are 2 possibilities, the first is when the distance traveled by 2 people is less than the full length, there is (

In the second case of x=1, when the distance traveled by 2 people is greater than the full length, that is, after A and B meet, they continue to drive, and there is at this time.

The solution is x=3, so when x=1 or 3, A and B are kilometers apart.

Example: The first time is a kilometer apart.

Let the two people be kilometers apart from each other for hours, according to the title.

Solution x=1

Example 2: The second time is kilometers apart.

Let the two people be kilometers apart from each other for hours, according to the title.

Solve x=3

A: After 1 hour or 3 hours, the two people are kilometers apart

(1) The two have never met.

So x = 1 hour.

2) The two have met and missed, back to back apart.

then x = 3 hours.

1.Solution: 12 has 3/8 divided by 4 has 1/2 equals 1/4

12 has three-eighths divided by two, and three-fourths equals 9/2

So, the fox can only fall into the fourth trap when it jumps into it, and the weasel falls into it when it jumps into the second trap.

When the weasel falls in, the fox jumps 4, and 1/2 times 2 equals 9 meters.

2.Let A do it alone for one day to complete project X, B can do it alone for one day to complete Project Y, and C can do it alone for one day to complete Project Z

x+y=11/60

y+z=3/20

x+z=1/6

x=1 10 y=1 12 z=1 15 A engineering team is the fastest.

x+y+z=1 4 So the three teams A, B, and C can work together to complete the project in one day 1 4

The bottom is Y, and the waist is X

The midline on the waist divides the circumference of this triangle into two parts: x+x2 and y+x2

i.e. x+x 2=3x 2=15, y+x 2=18 or 3x 2=18, y+x 2=15

then x=10, y=13 or x=12, y=9

Because of the group teasing, it is 10+10>13,12+12>9

So they can all collapse and sell to form a triangle.

So the bottom length is 13cm or 9cm

1.Let the original price be x, x=25a 18

The daily profit of processing A parts is 60a yuan.

The factors of 171 are 1,3,9,19,57,171

1, then 171-5=166

There are 166 fractions in the simplest truth.

1) When vertical, there is (2,-1)*(x,3)=2x-3=0Therefore, when the ridge is x=parallel, there are 2 x=-1 3 cherry coarse fibers with x=-62)(a+b)*(a-b)=(3,6)*(1,2)=3+12=153) and x as their angle.

a*b=|a|*|b|*cosx a*b=(3,0)*(4,-4)=12 |a|*|b|= 3*4 times the lower heel number 2

So cosx=(root number2) stool bi2 x=45, so their angle is 45 degrees.