Answer:
-9
Step-by-step explanation:
The sum of -2 and -7 is given as follows;
-2 + (-7)
In mathematical operations, +  *  - is -. 
So we have;
-2 - 7
This gives us: -9
 
        
             
        
        
        
49/8=6 (nearest whole number)
        
                    
             
        
        
        
C) x = -19/10 because when solving it with substitution u get x=-19/10 & y=153/10
        
             
        
        
        
Answer:
a =3 
b = -5
c = 4
Step-by-step explanation:
3x^2+4=5x
Subtract 5x from each side
3x^2-5x+4=5x-5x
3x^2-5x+4=0
The equation is in the form
ax^2 +bx+c =0
a =3 
b = -5
c = 4
 
        
             
        
        
        
Answer:
M = 1/0.000121 = 8264.5 years
Step-by-step explanation:
M = − k ∫∞₀ teᵏᵗdt
To obtain this mean life, we'll use integration by parts to integrate the function ∫ teᵏᵗdt
∫udv = uv - ∫ vdu
u = t
du/dt = 1
du = dt
∫ dv = ∫ eᵏᵗdt
v = eᵏᵗ/k
∫udv = ∫ teᵏᵗdt
uv = teᵏᵗ/k
∫ vdu = eᵏᵗ/k
∫ teᵏᵗdt = (teᵏᵗ/k) - ∫eᵏᵗ/k
But, ∫eᵏᵗ/k = (1/k) ∫eᵏᵗ = (1/k²) eᵏᵗ = eᵏᵗ/k²
∫ teᵏᵗdt = (teᵏᵗ/k) - eᵏᵗ/k²
The rest of the calculation is done on paper in the image attached to this question