DOC: Add formula renderings to integrate.nquad. (#15973)
DOC: Add formula renderings to integrate.nquad. (#15973)

* DOC: Add formula renderings to integrate.nquad.

* Correct le to leq

* fit to 80 characters in a line.

* Clean the code

* change """ to r"""

* fit to 80 characters in a line.
Stefan-Endres/scipy,perimosocordiae/scipy,rgommers/scipy,perimosocordiae/scipy,mdhaber/scipy,WarrenWeckesser/scipy,anntzer/scipy,mdhaber/scipy,endolith/scipy,Stefan-Endres/scipy,Stefan-Endres/scipy,rgommers/scipy,WarrenWeckesser/scipy,mdhaber/scipy,ilayn/scipy,rgommers/scipy,anntzer/scipy,mdhaber/scipy,WarrenWeckesser/scipy,scipy/scipy,ilayn/scipy,perimosocordiae/scipy,ilayn/scipy,anntzer/scipy,Stefan-Endres/scipy,mdhaber/scipy,scipy/scipy,WarrenWeckesser/scipy,scipy/scipy,ilayn/scipy,andyfaff/scipy,anntzer/scipy,andyfaff/scipy,endolith/scipy,mdhaber/scipy,scipy/scipy,rgommers/scipy,endolith/scipy,WarrenWeckesser/scipy,endolith/scipy,scipy/scipy,ilayn/scipy,anntzer/scipy,andyfaff/scipy,perimosocordiae/scipy,anntzer/scipy,rgommers/scipy,andyfaff/scipy,endolith/scipy,perimosocordiae/scipy,WarrenWeckesser/scipy,andyfaff/scipy,perimosocordiae/scipy,Stefan-Endres/scipy,scipy/scipy,ilayn/scipy,endolith/scipy,Stefan-Endres/scipy,andyfaff/scipy