The product of 14x25x4 is 1400 but I don't understand why you put use subtraction.
{-2x+y=12 => y=12+2x
{3x+2y=38
3x+2(12+2x)=38
3x+24+4x=38 /-24
7x=14 /:7
x=2
y=12+2*2=12+4=16
y=16
<em>Solution: (2; 16)</em>
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To ease the understanding, let's write it in degrees and not in Radian:
Formula of conversion: Degree°/180 = Radian/π
Convert 7π/4 in degrees: = (7x180)/4 = 315°
This angle is in the IV th Quadrant of the UNIT circle. So you can write 315° or - 45° .
sin(7π/4) = sin(315°) = sin( - 45°) = - sin(45°) = - (√2)/2
Answer: -3 and -4
Step-by-step explanation: