Answer:
a.
![M(x,y) = (-1,-1)](https://img.qammunity.org/2021/formulas/mathematics/high-school/yoirw3ju8pry9axxn6q9otek7fw4q63evb.png)
b.
![D(-4,-9)](https://img.qammunity.org/2021/formulas/mathematics/high-school/nf49d86ugptjz9f18l7tuhl6lstsjhpdi8.png)
Explanation:
Given
A(-8,7) and B(6,-9).
Solving (a):
Determine the Midpoint M;
This is calculated as follows;
![M(x,y) = ((x_1+x_2)/(2),(y_1+y_2)/(2))](https://img.qammunity.org/2021/formulas/mathematics/high-school/ti9jgfnf3q8x7xwkau1rer6ckwzxwvsjj6.png)
Where
![(x_1,y_1) = (-8,7)](https://img.qammunity.org/2021/formulas/mathematics/high-school/mdegnp6p0xt7o9tqf428sq9osdavzow4mv.png)
![(x_2,y_2) = (6,-9)](https://img.qammunity.org/2021/formulas/mathematics/high-school/2c4fxjp7k34io27lsx20qicl4baolysqh1.png)
Substitute these values in the formula
![M(x,y) = ((-8+6)/(2),(7-9)/(2))](https://img.qammunity.org/2021/formulas/mathematics/high-school/tsug9r5qk5zys3usljm12gy6qgk47ais1d.png)
![M(x,y) = ((-2)/(2),(-2)/(2))](https://img.qammunity.org/2021/formulas/mathematics/high-school/1wgtid8nwheuc4hj4z0wt04qtjffzi120k.png)
![M(x,y) = (-1,-1)](https://img.qammunity.org/2021/formulas/mathematics/high-school/yoirw3ju8pry9axxn6q9otek7fw4q63evb.png)
Hence; the midpoint is (-1,-1)
Solving (a):
Here, we have
C = (2,7)
M; Midpoint = (-1,-1)
Required: Determine D
This is calculated as follows;
![M(x,y) = ((x_1+x_2)/(2),(y_1+y_2)/(2))](https://img.qammunity.org/2021/formulas/mathematics/high-school/ti9jgfnf3q8x7xwkau1rer6ckwzxwvsjj6.png)
Where
![(x_1,y_1) = (2,7)](https://img.qammunity.org/2021/formulas/mathematics/high-school/3sqhu5jzhhcwjzg9tcst3r33z90e44hu67.png)
![(x,y) = (-1,-1)](https://img.qammunity.org/2021/formulas/mathematics/high-school/5tn5ej0lrwch00uid22jvmnjyj89owkrd1.png)
Substitute these values in the formula
![(-1,-1) = ((2+x_2)/(2),(7+y_2)/(2))](https://img.qammunity.org/2021/formulas/mathematics/high-school/mtizh6ahzby94ajdm1ex4938aa0u32g811.png)
Solving for x2
![-1 = (2 + x_2)/(2)](https://img.qammunity.org/2021/formulas/mathematics/high-school/9fq5xmyxwqzb63hgqhd78a3y1h7em0g5za.png)
Multiply both sides by 2
![-2 = 2 + x_2](https://img.qammunity.org/2021/formulas/mathematics/high-school/uqelsrtdm793vuybqimwcz5m417s84xk3k.png)
Subtract 2 from both sides
![x_2 = -2 - 2](https://img.qammunity.org/2021/formulas/mathematics/high-school/zs1ctmw9x3goxtnr7aw971xxm1zg7oqlov.png)
![x_2 = -4](https://img.qammunity.org/2021/formulas/mathematics/high-school/rvu8rnpghkr3ssowu97o8fped67qja6fzf.png)
Solving for y2
![-1 = (7 + y_2)/(2)](https://img.qammunity.org/2021/formulas/mathematics/high-school/kptdk9skavrmfj63c36ts96ih9ed99jhkc.png)
Multiply both sides by 2
![-2 = 7 + y_2](https://img.qammunity.org/2021/formulas/mathematics/high-school/2ci0kjyjbv41gqi1fz7al77rjl9ty02688.png)
Subtract 7 from both sides
![y_2 = -2 - 7](https://img.qammunity.org/2021/formulas/mathematics/high-school/41nrx68bufeqtmdss668j0fyjtnp4cxf0m.png)
![y_2 = -9](https://img.qammunity.org/2021/formulas/mathematics/high-school/bnlda4r5ubsetfrn634fsx0xaw89rcy2e6.png)
Hence, the coordinates of D is
![D(-4,-9)](https://img.qammunity.org/2021/formulas/mathematics/high-school/nf49d86ugptjz9f18l7tuhl6lstsjhpdi8.png)