They are separate questions. A variable s increased by 2:
The sum of a and b:
c minus the sum of a and b :
z increased by 12
t minus the sum of s and 5:
The sum of 15 and d then decreased by c:

S+2,  

a+b,  

c-(a+b),

z+12,

t- (s+5) ,

(15+d) -c

Step-by-step explanation:

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step-by-step explanation:

x = ±sqrt(10)

step-by-step explanation:

5 - 2x² = -15

subtract 5 from each side

5-5 - 2x² = -15-5

-2x^2   = -20

divide by -2 on each side

-2x^2   /-2= -20/-2

x^2 =10

take the square root on each side

sqrt(x^2 )=±sqrt(10)

x = ±sqrt(10)

check:

5 - 2x² = -15

+sqrt(10)

5 - 2(sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15

-sqrt(10)

5 - 2(-sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15