# Post-Homework Death 570 Points```My math teacher made me do this so now I'm forcing you to do this too.
Flag is all lowercase; replace spaces with underscores.
Dev: ClaireHint! When placing the string in the matrix go up to down rather than left to right.Hint! Google matrix multiplication properties if you're stuck.```[posthomeworkdeaths.txt](posthomeworkdeaths.txt)
Inside the text file:```Decoding matrix:
1.6  -1.4  1.82.2  -1.8  1.6-1     1    -1
String:
37 36 -1 34 27 -7 160 237 56 58 110 44 66 93 22 143 210 49 11 33 22```
Its just a simple [matrix multiplication](https://www.mathsisfun.com/algebra/matrix-multiplying.html)
Assume the `Matrix A` is Decode matrix and `Matrix B` is String Matrix``` According to the hint, we place string up to down so become 3X7 Matrix
     Matrix A                  Matrix B | 1.6  -1.4  1.8 |   | 37 34 160  58 66 143 11 | | 2.2  -1.8  1.6 | X | 36 27 237 110 93 210 33 || -1     1    -1 |   | -1 -7  56  44 22  49 22 |```I wrote a [python script](solve.py) to calculate:```pyimport numpy as npA = np.array([[1.6 ,-1.4  ,1.8],			 [2.2  ,-1.8  ,1.6],			 [-1 , 1 , -1]])
B = np.array([[37, 34, 160, 58, 66, 143, 11],			 [36 ,27 ,237 ,110 ,93 ,210 ,33],			 [-1 ,-7, 56 ,44, 22, 49, 22]])
C = np.dot(A,B)print(C)```Result:```[[7.00000000e+00 4.00000000e+00 2.50000000e+01 1.80000000e+01  1.50000000e+01 2.30000000e+01 1.10000000e+01] [1.50000000e+01 1.50000000e+01 1.50000000e+01 1.42108547e-14  1.30000000e+01 1.50000000e+01 7.10542736e-15] [0.00000000e+00 0.00000000e+00 2.10000000e+01 8.00000000e+00  5.00000000e+00 1.80000000e+01 0.00000000e+00]]```
Search `Decode Matrix` on Google, I saw [this page](https://www.instructables.com/id/Encrypt-a-message-using-matrixes/) says 1-26 is A-Z and 0 is space
Then I add few lines of code below:```pyflag = ""for i in range(7):	for j in range(3):		f = int(C[j][i])		if f == 0:			flag += "_"		else:			flag += chr(f+97)print(flag)```Result:```HP_EP_ZOVS_IPNFXPSL__```Emm seems is encrypted, lets try caesar cipher!```+1	go_do_ynur_homework__+7	ai_xi_shol_bigyqile__+11	we_te_odkh_xecumeha__+22	lt_it_dszw_mtrjbtwp__......```Can see the **first one** is the flag! (Don't know why is abit off)
## Flag ```rtcp{go_do_your_homework}```