\(=>Qthu1=0,2.340000=68000J\)

\(=>Qthu2=2100.0,2.20=8400J\)

\(=>Qtoa=2.4200.25=210000J\)

\(=>Qthu1+Qthu2< Qtoa\)=>đá nóng chảy hoàn toàn

\(=>0,2.2100.20+0,2.340000+0,2.4200.tcb=2.4200\left(25-tcb\right)\)

\(=>tcb=14,5^oC\)

Cho em hỏi ngu tí ạ vậy tcb ở nhưng phép tính trên vứt đi đâu ạ 

a: \(A=4-\sin^245^0+2\cdot cos^260^0-3\cdot\cot^345^0\)

\(=4-\left(\frac{\sqrt2}{2}\right)^2+2\cdot\left(\frac12\right)^2-3\cdot1^3\)

\(=4-\frac12+2\cdot\frac14-3=4-3=1\)

b: \(B=tan45^0\cdot cos30^0\cdot\cot30^0\)

\(=1\cdot\frac{\sqrt3}{2}\cdot\sqrt3=\frac32\)

c: \(C=cos^215^0+cos^225^0+\cdots+cos^275^0\)

\(=\left(cos^215^0+cos^275^0\right)+\left(cos^225^0+cos^265^0\right)+\left(cos^235^0+cos^255^0\right)+cos^245^0\)

\(=1+1+1+\left(\frac{\sqrt2}{2}\right)^2=3+\frac12=\frac72\)

d: \(D=\sin^210^0+\sin^220^0+\cdots+\sin^280^0\)

\(=\left(\sin^210^0+\sin^280^0\right)+\left(\sin^220^0+\sin^270^0\right)+\left(\sin^230^0+\sin^260^0\right)+\left(\sin^240^0+\sin^250^0\right)\)

=1+1+1+1

=4

Ban can cau nao nhi?

làm bài nào??

36B

37C

38D

39B

40D

41A

42B

43B

44A

45B

46B

47A

48C

50B

51B

52B

53D

54C

55D

56C

3.15:
EF vuông góc MH

NP vuông góc MH

Do đó: EF//NP

3.17:

góc yKH+góc H=180 độ

mà hai góc này là hai góc ở vị trí trong cùng phía

nên Ky//Hx

1.Yes, they do

2..Yes, it is

3.People buy fruits and flowers from the market and decorate their house

4.People visit their family and friends